This invention relates to inverter-type power sources for transforming an AC (alternating current) voltage of a first magnitude to an AC voltage of a second magnitude suitable for driving a load such as a set of lamps or other household appliance. More particularly, the invention relates to a power converter comprising an inverter circuit which minimizes dissipation of power within components of the circuit, to permit a sufficient size reduction for unobtrusive mounting of the converter within an appliance fixture such as a track-lighting fixture.
Transformers have been employed for converting household voltage, for example 110 VAC 60 hertz, to a lower voltage such as 12 VAC for operating an appliance or other electrical load such as a lamp. However, the physical size of a transformer is dependent on the frequency of the alternating current and, at the usual frequency of household electric supply, tends to be too large to accommodate the transformer within an appliance. Accordingly, more modern power conversion devices employ an inverter circuit which includes a transformer and an oscillator operating at substantially higher frequencies so as to minimize the size of the transformer. The physical size of such power conversion devices is dependent on the size of the transformer plus other components such as transistors, capacitors, and any cooling devices such as fins which may be required.
A situation of particular interest is the deployment of a low-voltage power converter in a track lighting fixture. In such lighting fixtures, all the components thereof including the lamp, the track, and a device for securing the lamp to the track are visible, and must be esthetically pleasing for use in the home and in business establishments.
If it is desired to employ lamps which operate on a low voltage, such as 12 volts, it is necessary to provide a transformer or converter for the incoming house voltage of 110-120 volts to reduce the house voltage to the 12 volts required by the lamp. It would be most convenient if such a converter could be physically connected to the lamp in the track lighting fixture because such an arrangement of components would facilitate installation of the track lighting fixture.
The requirement of an esthetic appearance necessitates that the physical configuration of the converter present a relatively small package, of low profile so that the package is less visible and less intrusive to people utilizing the track lighting fixture. Such reduced size can only be accomplished by the use of relatively small electrical components on the converter, and by the construction of a circuit which minimizes the amount of power dissipated within the converter. It is readily apparent that excessive power dissipation within the converter would necessitate special cooling arrangements, such as external fins, and may also necessitate larger circuit components for handling increased power.
A problem that arises in existing circuits is that they do not minimize power dissipation within the electrical components to the fullest extent possible. As a result, attempts to include existing power sources or converters within a track lighting fixture, or other appliance having a high visibility location, without being obtrusive are not usually successful.